You have only a certain number of lives (except on Easy), take your time

Use your character's special ability when you need it

The weapons are great for destroying things fast

If you fail a mission, don't panic. Use it as experience, or better yet, experience point. Hardcore gives you more points for the things you destroy, and you can use that to level your characters up quickly

Always move around enemies. This prevents them from hitting you, and you need all the health you can keep

When you kill an enemy, they will sometimes drop green boxes which are health. This is a key factor for survival

When you kill an enemy, they will sometimes drop red boxes which are ammunition for your weapon. This is a key factor for killing enemies with ease

When you kill an enemy, they will sometimes drop blue boxes which upgrade your primary weapon . When you get 2, you will have it maxed (unless you have upgraded the amount). You will deal more damage with the more upgrades you collect.

Completing Secondary Objectives earn you trophies, as well as a great deal of points. Complete them for an easier way to level up, and earn The Daily Grind

Circle around tanks, and other rocket-shooting vehicles to make sure you don't get damaged by the rockets

Choose one character and stick with it. Upgrade your character to fit your needs

Throughout the levels, there are hidden lives that you can collect to add to the amount of lives you have left. They look like hearts with wings

Step 1: Beat the game on Medium
This will give you practice so you can beat the game on Hardcore later on. Make sure to finish all of the secondary objectives and finish the game on Medium to unlock the following trophies:

Goody Two Shoes

Airborne

A Mess of Stiff Staff Sergeants

Jonesing for Relics

From Cold Dead Hands

Supply Problems

Inferno's Briefs

To Hell And Back

The Daily Grind

Step 2: Beat the game on Hardcore
Beat the game with all of the techniques and strategies you picked up during you Medium playthrough and apply them to Hardcore. Reply missions for a higher skill score, and try to get a big damage streak to unlock the following trophies:

Goody Two ShoesBring 20 Prisoners to the Church in single player

In Mission 1: Baptism in Fire, you will get a Primary Objective to rescue a prisoner. Shoot the crate he is in, and take him to the church. After that, you will get a Secondary Objective (grey arrow) to go and rescue more. Once you rescue 20, this trophy is yours. You will have to stray away from the Primary Objectives to complete this. If you have to destroy the tanks, you have missed this trophy and will have to replay the mission. You can select it from the menus.

AirbornePilot a helicopter in single player

This Trophy Is Story-Related and Cannot Be Missed

In Mission 1: Baptism in Fire, after you destroy the tanks as a Primary Objective, you will get a crate sent down to you. Shoot it open and drive into the helicopter and you will begin to fly it, thus unlocking this trophy.

Note: Mission 1 is not the only time you will fly a helicopter, but it is the only time where it isn't optional. Mission 1 will be the first place you get the trophy, but there are others as well.

A Mess of Stiff Staff SargeantsKill Inferno's Sergeants in single player

In Mission 2: Moths to the Flame, you will eventually come across a Secondary Objective (grey arrow) that will tell you to kill the Sergeants that stand in the way. This is fairly simple to get while you focus on the Primary Objective, you will have to break away from it a few times. Sergeants are in small trucks, surrounded by other military trucks. Once you kill them all, you will have completed the Secondary Objective and obtained this trophy.

Jonesing for RelicsReturn all the Relics to the Museum in single player

In Mission 3: The Phoenix's Nest you will have a Secondary Objective (grey arrow) to collect the relics. These are in crates that you have to shoot open. Drive into them to collect them. There are many scattered throughout the map, so just follow your arrow to each. Most are on the same path as the Primary Objectives anyway, so they shouldn't be a hassle.

From Cold Dead HandsSteal all Inferno's Weapon Crates in single player

In Mission 4: Fire Hazard you will get a Secondary Objective (grey arrow) to arm civilians. You will need to get about 9-12 weapons and bring them back to the village. Once you have collected them all and brought them back, this trophy will unlock.

Supply ProblemsDestroy all Mining Carts in the Kaabe Mountains in single player

In Mission 6: The Cauldron you will get a Secondary Objective to destroy the mining carts. These are easy to destroy, but the first 2 are on mini-trains that you will need to destroy. The rest are all along the Primary Objective path so there is no need to worry about these. Once you destroy them all this trophy is yours.

Inferno's BriefsSteal all the Document Briefs in single player

In Mission 8: From the Ashes you are tasks with a Secondary Objective to collect all of the Intel briefs. There many all around the map, but they are all on the path of the Primary Objective, so they are all extremely easy to collect. Once you collect them all this trophy will pop.

To Hell and BackComplete Mission 9 on any Difficulty in single player

This Trophy Is Story-Related and Cannot Be Missed

In Mission 9: The Furnace, you will be playing through the final mission. In this level, you will have your final face-off with Inferno. As simple as it sounds, all you need to do is beat the final mission to unlock this trophy.

Inferno is a huge pain in the ass at the very end. But, a good strategy is to stay far away from him, so you don't get hit by the flame-throwers. Keep destroying the helicopters for more health and ammo. Once his health is depleted fully this you will have beaten the mission.

Tough StuffComplete all missions on Hardcore Difficulty

Hardcore is the hardest difficulty in the game, and is available from the beginning. When trying to complete this, keep the following tips in mind.

You have only 3 lives, take your time

Use your character's special ability when you need it

The weapons are great for destroying things fast

If you fail a mission, don't panic. Use it as experience, or better yet, experience point. Hardcore gives you more points for the things you destroy, and you can use that to level your characters up quickly

Always move around enemies. This prevents them from hitting you, and you need all the health you can keep

When you kill an enemy, they will sometimes drop green boxes which are health. This is a key factor for survival

When you kill an enemy, they will sometimes drop red boxes which are ammunition for your weapon. This is a key factor for killing enemies with ease

When you kill an enemy, they will sometimes drop blue boxes which upgrade your primary weapon . When you get 2, you will have it maxed (unless you have upgraded the amount). You will deal more damage with the more upgrades you collect.

The Daily GrindGet a character to max level

In each level, you get points for killing enemies and blowing stuff up. These all add up to your total, at the top left hand corner of the HUD. This is XP that increases your level for a certain character. Choose any character and stick with him/her throughout the game. Once you reach level 45, this trophy will pop. You can see what level you are at in the character selection menu, under their name. Get multipliers by killing things in rapid succession, if you see a x50, you will also unlock Mega Kill Combo.

Mega Kill ComboGet a 50x Damage Streak in single player

Whenever you damage/kill many things quickly, you will see a multiplier under a bar that recedes when you don't cause damage. In the later levels, you will have the chance to rack up the multiplier really high. When you see the bar recede, shoot whatever you can to make sure you keep the multiplier.

Once you see it at x50, you will unlock this trophy and earn a lot of points. So just keep randomly shooting everything in the later levels and you should get this without too much problem. It is easier to get this on Hardcore, but if you find a good spot on Medium then use that.

Note: This is not possible to earn on Easy, you don't get points on Easy, therefore you don't get multipliers.